The present invention relates to a method and apparatus for recording optical information; and, more particularly, to a method and apparatus capable of recording optical information at high speed without increasing the laser power required in forming pits.
An optical recording technique has been widely used in storing a large volume of information, in which the information is optically recorded in an optical information recording medium, e.g., such an optical disk as CD-recordable (CD-R) or the like. Recently, there has been introduced a technique to record the optical information at a speed of or beyond 2 to 6 times the standard recording speed.
Recording of information on the optical disc is accomplished by irradiating a pulsed laser beam on the rotating optical disc based on a digital signal, which has been obtained by digitizing the information to be recorded, to thereby form pits on the disk.
In order to form the pits on the optical disc based on the digital signal, a high intensity laser beam is irradiated on the optical disc during a high level of the digital signal, wherein the laser power causes the change of states of the irradiated recording layer to form the pits. During a low level of the digital signal, a low intensity laser beam required for tracking is irradiated on the disk.
High speed recording can be achieved by rotating an optical disk at an increased speed and reducing the period of a digital signal according to the rotational speed of the disc.
In case of a dye-based recordable optical disc, pits are formed on a recording layer of the optical disc by the thermal energy delivered by the irradiated laser beam. Accordingly, if an intensity of the laser beam is not sufficient enough, the high speed recording of the optical information may result in the formation of incomplete pits or no pit formation at all.
To be specific, the intensity of the laser beam irradiated on the optical disc varies according to the digital signal as illustrated in FIG. 2. For instance, if the intensity of the laser beam being irradiated on the optical disc is set to be high during the high level H of the digital signal, the thermal energy delivered to the optical disc gradually increases while the high intensity laser beam is provided and starts to decrease gradually once the intensity of the laser beam becomes low. Pits are formed on portions of the recording layer exposed to a temperature equal to or greater than a threshold temperature, at which change of states of the recording layer begins to occur.
An excessive portion of the thermal energy supplied to form a pit is transferred to and dissipated in the surrounding region of the pit, serving to preheat a portion of the recording layer in which a next pit is to be formed.
However, as a relative velocity between the optical disc and a laser beam source increases with an increase of a rotational speed of the optical disc, the excessive thermal energy provided by the thermal energy supplied by the irradiation of the laser beam onto the optical disc decreases as shown in FIG. 3, which in turn often results in incomplete pit formation or no pit formation at all. Consequently, it has been required to increase the laser power for the formation of the proper pits with the increasing relative velocity, necessitating a costly high power laser.
It is, therefore, an object of the present invention to provide a method and apparatus capable of recording optical information at high speeds without employing a high power laser.
In accordance with an aspect of the present invention, there is provided a method for recording optical information on an optical information recording medium, wherein optically detectable pits and lands having various lengths are formed by thermal energy provided by a pulsed laser beam irradiated on the optical information recording medium by a light source which has a first intensity level for forming a pit and a second intensity level for forming a land, the second intensity level being lower than the first intensity level, characterized in that
the second intensity level is set corresponding to linear velocity of the medium.
In accordance with another aspect of the present invention, there is provided an apparatus for recording optical information on an optical information recording medium, wherein optically detectable pits and lands having various lengths are formed by thermal energy provided by a pulsed laser beam which has a first intensity level for forming a pit and a second intensity level for forming a land, the second intensity level being lower than the first intensity level, the apparatus comprising:
a light source for generating the laser beam; and
second intensity setting means for setting the second intensity level corresponding to linear velocity of the medium.